A study is being undertaken to investigate endosymbiosis at the level of control of macromolecular synthesis. The experimental organisms to be used is the association between the biflagellated protist Cyanophora paradoxa and its endosymbiotic blue-green algae Cyanocyta korchikoffiana. Since this association represents a symbiosis between a prokaryote and an eukaryote, it is intended to take advantage of the specific sensitivities of these organisms to antibiotics to determine to what extent, and by what mechanisms the host regulates synthetic processes in the symbiont. This study is viewed as one which could give us insight into fundamental aspects of mechanisms of "biological integration", ranging from parasitism to mutualism.